Timing control



July 4, 1939.

OUTPUT A. PFISTER TIMING CONTROL Filed June 15, 1936 SIGNAL Indn10 l l l l CONTROL INPUT g I o- I g 0 INVENTOR Akl'hur Pfisfer.

I I I NEY Patented July 4, 1939 UNITED STATES PATENT OFFICE TIMING CONTROL Jr., Gloucester, Mass.

Application June 15, 1936, Serial No. 85,283

10 Claims.

This invention relates to a timing system for controlling the rates of increase and decrease of electrical energy in a utilization circuit and more particularly to a system for controlling the rates 5 of charge and discharge of an electrical condenser.

This application is a continuation in part of my copending application Serial No. 735,190 filed July 14, 1934, for Sound translating system, now Patent No. 2,052,110.

An object of this invention is to provide means for separately controlling the rates of crescendo and decrescendo in an audio frequency amplifier.

Another object is to provide means for separately controlling the rates of energy increase and energy decrease in a transmission channel.

Another object is to provide a system of the above type in which the timing may be easily adjusted.

20 Another object is to provide a relatively simple, dependable and eflicient device for the above purposes.

Various other objects and advantages will be apparent as the nature of the invention is more 25 fully disclosed.

The invention also consists in certain new and original features of construction and combination of parts hereinafter set forth and claimed.

Although the novel features which are believed to be characteristic of this invention will be particularly pointed out in the claims appended hereto, the invention itself, as to its objects and advantages, and the manner in which it may be carried out, may be better understood by referring to the following description taken in connection with the accompanying drawing forming a part thereof in which The figure shows an embodiment of the invention in a sound reproducing system.

In the following description and in the claims, various details will be identified by specific names for convenience, but they are intended to be as generic in their application as the art will permit.

In the drawing accompanying and forming part of this specification, certain specific disclosure of the invention is made for purposes of explanation, but it will be understood that the details may be modified in various respects without departure from the broad aspect of the invention.

Referring to the embodiment illustrated in the drawing, a signal input device I is shown, which may comprise a sound pickup device, transmission line or the like with the necessary amplifiers. The signal input device I is coupled by a coupling transformer 2, to an amplifier stage 3 having a pair of double-grid, space discharge tubes 4 connected in push-pull relationship. The output of the amplifier stage 3 is sup- 5 plied to an output device 5 through a coupling transformer 6. The output device 5 may comprise a loud speaker or a transmission line with the necessary amplifiers incorporated therewith in the usual manner and as shown more in detail in the copending application above mentioned.

More specifically, the terminals of the secondary winding I of transformer 2 are connected to the second or signal grids I l of the tubes 4 and the center tap [2 of the secondary I0 is connected, by a biasing battery l3, to the cathodes M of said tubes. The anodes l5 are connected to the primary l6 of the transformer 6. Plate voltage is supplied by a battery l'I connected between the cathode l4 and a center tap l8 of the primary IS.

The first or control grids 20 are connected to the output circuit 2| of a control channel, as will be more fully described later. By connecting the input circuit to the second grids II (as shown) distortion will be kept at a minimum. It is quite feasible, however, and within the scope of the present invention, to connect the signal input circuit to the first grids and the control circuit to second grids ll.

Transformer 6 is designed with certain desired frequency characteristics whereby it will act as a band-suppression filter at low signal volumes to reduce the transmission of the intermediate frequency registers to a greater extent than the high and low registers. At high signal intensities, however, the transformer has substantially uniform efliciency throughout the audible frequency range.

A filter network 25, comprising a series connected condenser 26 and inductance 21, and a parallel resistor 28, may be connected across the primary l6 of the transformer 6 to obtain the desired frequency response. This filter network works in conjunction with the tube output impedance to discriminate against the intermediate frequencies more at low volume levels.

The control channel has its input circuit 30 connected by a,transformer 3| to an amplifier stage 32 comprising a pair of vacuum tubes 33 connected in push-pull relationship.

The output of the amplifier 32 includes the primary 34 of a transformer 35 the secondary winding 36 of which is connected to the anodes of a pair of two element thermionic tubes 3?, together comprising a full-wave rectifier 88.

The center of secondary winding 36 and the cathodes of tubes 3? are connected to opposite ends of resistance Ml, which will hereinafter be called the control resistance. Current from rectifier 38 will pass through control resistance ii! in the direction of the arrow, rendering the upper end of the resistance (as seen in the drawing) positive with respect to the lower end.

Connected in parallel with resistance at is a condenser 4| which serves as a filter for the audiofrequency fluctuations in the rectified current from rectifier 38. The current through resistance 40 will thus be averaged to represent the envelope of the rectified currents or, in other words, the intensity of the signal received from the control input circuit 30.

A variable delay arrangement is associated with output circuit 2! of the control channel. This delay arrangement comprises a resistance d2 connected in output circuit 2i and a variable condenser 43 connected across both resistances All and 42. These elements form a condenser-resistance discharge device the inertial characteristics of which may be varied by adjusting variable condenser 43.

Connected in parallel with resistance 42 are two three-element vacuum tubes 65 and 46. These tubes are connected in parallel opposing relation, that is, the anode of tube 45 and the cathode of tube 46 are both connected to one end of resistance 42 and the cathode of 45 and anode of 46 to the other end of resistance 52. The grid elements of tubes 45 and M3 are connected respectively, to sliding contacts il and 58 arranged to slide on resistance ,2. Thus the grid biases of the tubes may be varied independently to regulate the individual internal impedance of these tubes. The inertial or delay action may thus be separately regulated for buildup and decay of potential across output circuit 2i.

Control resistance ill comprises part of the output circuit 2! of the control channel. The entire output circuit includes the following elements in series: control grids 2B of amplifier 3, resistance 42, control resistance ill, biasing potentiometer 50 and cathodes M- of amplifier 3. A biasing battery 5! is connected in parallel with potentiometer 58 to furnish a potential gradient across the potentiometer. The normal or initial bias on control grids 20 may be adjusted by moving a sliding contact 52 along the potentiometer 50.

A discharge device 53 is connected across control resistance All and serves to limit the potential which can be developed across this resistance. The cathode of this tube is connected to a sliding contact 53a on a potentiometer 5 3 which is connected across biasing battery 5i in the same manner as potentiometer 50.

The anode of tube 53 is connected to the positive end of control resistance iil. The grid of tube 53 is connected to a contact 55 arranged to slide on control resistance lil.

Operation In the operation of this system, the sound energy from the signal input device l passes through transformer 2 and is amplified by amplifier 3 Whose gain ratio is varied by the control grids 2B.

The control of the gain ratio is brought about as follows: Control energy from any control source, such as a separate control channel, or derived from the signal input device l, is amplified by push-pull amplifier 322, the output of which passes through transformer 35 and is rectified by full wave rectifier 38 to yield a direct current which passes through control resistance 40 from the cathodes of rectifier 38 to the center of secondary winding 35 of the transformer 35. It will be obvious that the average strength of this direct current over any limited interval will be directly proportional to the strength of the control input. Condenser ii serves to filter out the audio-frequency fluctuations of the rectified current. The current through resistance ill will then represent an envelope of the rectified current impulses.

The potential across resistance it will accordingly be varied along with the strength of the rectified current, the upper end of the resistance (as shown in the drawing) being made positive with respect to the lower end. This control potential opposes the biasing potential from bat- A tery 5!. Thus, an increase of control current will cause a decrease of negative bias on the control electrodes 29, thereby decreasing the impedance of the space discharge paths of tubes 6. The gain ratio of tubes 4 will accordingly be increased so that they will have a greater amplifying effect on the audio-frequency signals. The system has been described above as connected for volume expansion. It is to be understood, however, that the connections may be so made that volume compression is obtained, as, for example, for auto-- matic volume control purposes. By such control action the gain ratio of amplifier 3 may in some instances be varied over a range of 30 decibels between low and high control input values.

By adjusting contact 52 on potentiometer iiil the initial bias on the control electrodes and hence the initial amplification setting of the amplifier tubes 4 may be adjusted to any desired value.

Discharge tube 53 serves to limit the change in bias which the control circuit may produce on the control electrodes by controlling the percentage change in bias which the control channel may bring about for any control current.

With the setting of the potentiometer contacts 52 and 53a, as shown, the anode of limiting device 53 will be negatively biased with respect to its cathode as long as no current is passing through resistance 40. When current passes through resistance 40, thereby causing a potential drop in this resistance, the anode of device 513 will be made less negative and will occasionally become positive with respect to its cathode when the higher volumes are reached.

The anode of device 53 will thus become positive when the potential drop across resistance 49, determined by the volume of the control current, has reached a value sufficient to overcome the initial bias on the anode. When this potential value is reached, a discharge will begin between the anode and cathode of device 53, this device thereby serving to shunt a portion of the current received from rectifier 38.

While the anode or plate bias of tube 53 is varied by the change in total potential drop across control resistance Gil the grid bias of this tube may be varied as any fraction of the potential drop across the control resistance, This fraction is determined by setting sliding contact 55 to any desired point on the control resistance. Accordingly, device 53 will have a variable impedance, the value of which is determined by the potential drop across control resistance d0.

Thus by setting contacts 55 and 53 the potential drop across control resistance 4!], and hence the expansion characteristics of the amplifier 3, may be adjusted to correspond to any one of several desired functions of the control current.

During operation, sudden changes in control energy may occur. By variously delaying the change in gain ratio of the amplifier 3 when these changes in control occur, a more pleasing and natural effect will be obtained. The variable delay circuit permits separate adjustment of the delay for crescendo and decrescendo.

If a sudden increase in control current occurs, the potential drop across control resistance 40 will increase immediately. The change in potential applied to the control electrodes 20 will be delayed, however, due to the action of the variable delay circuit. The length of delay will depend on the capacity of condenser 43 and the impedance of tube 45. Likewise, on sudden decrease of control current, the potential drop across resistance 40 will decrease but the change in potential on the control electrodes 20 will be delayed. The length of delay will depend on the capacity of condenser 43 and the impedance of tube 46. Adjustment of the capacity of condenser 43 will accordingly vary the delay for both crescendo and decrescendo.

In addition, separate adjustment of delay on crescendo and decrescendo is afiorded by space discharge tubes 45 and 46. By adjusting contact 41 with respect to resistance 42, the shunting action of tube 45 for resistance 42 on crescendo will be varied. Similarly, by adjusting contact 48 with respect to resistance 42, the shunting action of tube 46 for this resistance on decrescendo will be varied. Thus the delay on crescendo and decrescendo may be adjusted by moving contacts 41 and 48 to separate values most desirable for the individual selection to be rendered.

For rapid attack or build up of amplification, contact 41 will be set near the lower end of resistance 42 and the impedance of tube 45 will be low. For slow attack or build up of amplification, the contact 41 will be set near the upper end of the resistance 42 and the impedance of tube 45 will be high. For intermediate rates of crescendo the contact 41 will be set at intermediate points on the resistance 42.

For rapid decay of the signal the contact 48 is set near the upper end of resistance 42, as shown in the drawing. For slow decay or falling off of amplification, the contact 48 would be set near the lower end of resistance 42. For intermediate rates of decrescendo intermediate setting of the contact .8 on the resistance 42 may be employed. The resistance 42, being in series with the resistance 4!], serves to maintain a given minimum impedance across the condenser 43 regardless of the impedance changes produced in the resistance 49 by means of the limiting device 53.

While an embodiment of the invention has been set forth for purposes of illustration, it is to be understood that the invention is not to be limited thereto, but is only to be limited in accordance with the following claims when interpreted in view of the prior art.

What I claim is:

1. In a system of the class described, a control circuit comprising a condenser, an impedance carrying a fluctuating unidirectional current, a second impedance, said impedances being connected in series in the charge and discharge path of said condenser and means causing said second impedance to have different values for charging current and for discharge current whereby different rates of charge and discharge are obtained.

2. In combination, a space discharge amplifier, an impedance connected to control the amplification ratio thereof, means to supply control energy to said impedance, and a timing circuit to control the rate of change of said energy, said timing circuit having adjustable means for controlling independently the rates of increase and of decrease of said energy.

3. In combination, a space discharge amplifier, an impedance connected to control the amplification ratio thereof, means to supply control energy to said impedance, and a timing circuit to control the rate of change of said energy, said timing circuit having means for controlling independently the rates of increase and of decrease of energy.

4. In combination, a space discharge amplifier having a control circuit including an impedance connected to control the amplification ratio thereof, means to supply control energy to said impedance, and a timing circuit to control the rate of change of said control energy, said timing circuit comprising, in series circuit, a capacity and a pair of oppositely poled, parallel rectifiers, said series circuit being connected across said impedance, said rectifiers being adapted to respectively control the rates of charge and discharge of said capacity.

5. A system of the class described comprising a control circuit including a capacity, a resistance connected in the charge and discharge path of said capacity and a pair of space discharge devices having their space current paths connected across said resistance and adapted to form opposite uni-directional shunts for controlling respectively the rates of charge and discharge of said condenser.

6. A system of the class described comprising a control circuit including a capacity, a resistance connected in the charge and discharge path of said capacity and a pair of space discharge devices having their space current paths connected in parallel across said resistance and adapted to form opposite uni-directional shunts there-across for controlling respectively the rates of charge and discharge of said condenser, said space discharge devices having control electrodes adjustably and independently connected to said resistance whereby the operating characteristics of said space discharge devices may be adjusted for independently varying the rate of charge and discharge of said capacity.

'1. In combination, an amplifier, a control circuit for varying the gain ratio of said amplifier and a timing circuit for varying the rate of change of the efiect produced by said control circuit, said timing circuit comprising 3; capacitance, a resistance connected to control the rate of charge and discharge thereof, a pair of uni-directional discharge devices oppositely connected in shunt across said resistance and means for separately adjusting the impedance of said devices.

8. In combination, a space discharge amplifier having a control electrode, a biasing resistance in the circuit of said control electrode, a second resistance in series with said biasing resistance, a capacitance in shunt with said two resistances, an impedance in shunt with said second resistance and means for independently varying the value of said impedance for charge and discharge respectively of said capacitance.

9. In combination, a space discharge amplifier having a control electrode, a biasing impedance for determining the bias on said control electrode, a control circuit for changing the potential across said impedance, means for delaying said change and means for separately varying the delay for increase and decrease of said potential.

10. In combination, a space discharge amplifier having a control electrode, a first resistance in the circuit of said control electrode, a second resistance in series with said first resistance, a capacitance in shunt with said two resistances and a variable impedance limiting device in shunt with said first resistance for limiting the potential drop therein, the second resistance being adapted to maintain a given minimum impedance across said condenser regardless of the impedance changes produced by the limiting device.

ARTHUR PFISTER. 

